1. Field of the Invention
This invention relates to microcell electrochemical devices and assemblies, methods of making same by various techniques, and use of such devices and assemblies.
2. Description of the Art
In the field of energy supplies and energy conversion devices, and particularly in the development of fuel cells and batteries, there has been continuing effort to develop devices with significant power outputs (high current and/or high voltage), high power density, and high energy output per unit volume.
Structurally, electrochemical cells such as batteries and fuel cells are relatively simple, utilizing respective positive and negative electrodes separated in such manner as to avoid internal short circuiting, and with the electrodes being arranged in contact with an electrolyte medium. By chemical reaction at the electrodes, the chemical energy of the reaction is converted into electrical energy with the flow of electrons providing power when the electrode circuit is coupled with an external load.
Battery cells may use separator plates between respective electrodes so that multiple sheet elements are arranged in successive face-to-face assemblies, and/or such sheets may be wound together in a (spiral) roll configuration.
The fuel cell is of significant current interest as a source of power for electrically powered vehicles, as well in distributed power generation applications.
In fuel cells, a fuel is introduced to contact with an electrode (anode) and oxidant is contacted with the other electrode (cathode) to establish a flow of positive and negative ions and generate a flow of electrons when an external load is coupled to the cell. The current output is controlled by a number of factors, including the catalyst (e.g., platinum in the case of hydrogen fuel cells) that is impregnated in the electrodes, as well as the kinetics of the particular fuel/oxidant electrochemical reaction.
Currently, single cell voltages for most fuel cells are in the range of about 0.6-0.8 volts. The operating voltage depends on the current; as current density increases, the voltage and cell efficiency correspondingly decline. At higher current densities, significant potential energy is converted to heat, thereby reducing the electrical energy of the cell.
Fuel cells also may be integrated with reformers, to provide an arrangement in which the reformer generates fuel such as hydrogen from natural gas, methanol or other feed stocks. The resulting fuel product from the reformer then is used in the fuel cell to generate electrical energy.
Numerous types of fuel cells have been described in the art. These include:
polymer electrolyte fuel cells, in which the electrolyte is a fluorinated sulfonic acid polymer or similar polymeric material;
alkaline fuel cells, using an electrolyte such as potassium hydroxide, in which the KOH electrolyte is retained in a matrix between electrodes including catalysts such as nickel, silver, metal oxide, spinel or noble metal;
phosphoric acid fuel cells using concentrated phosphoric acid as the electrolyte in high temperature operation;
molten salt fuel cells employing an electrolyte of alkali carbonates or sodium/potassium, in a ceramic matrix of lithium aluminate, operating at temperatures on the order of 600-700 degrees C., with the alkali electrolyte forming a high conductive molten salt;
solid oxide fuel cells utilizing metal oxides such as yttria-stabilized zirconia as the electrolyte and operating at high temperature to facilitate ionic conduction of oxygen between a cobalt-zirconia or nickel-zirconia anode, and a strontium-doped lanthanum manganate cathode.
Fuel cells exhibit relatively high efficiency and produce only low levels of gaseous/solid emissions. As a result of these characteristics, there is great current interest in them as energy conversion devices. Conventional fuel cell plants have efficiencies typically in the range of 40-55 percent based on the lower heating value (LHV) of the fuel that is used.
In addition to low environmental emissions, fuel cells operate at constant temperature, and heat from the electrochemical reaction is available for cogeneration applications, to increase overall efficiency. The efficiency of a fuel cell is substantially size-independent, and fuel cell designs thus are scalable over a wide range of electrical outputs, ranging from watts to megawatts.
A recent innovation in the electrochemical energy field is the development of microcellsxe2x80x94small-sized electrochemical cells for battery, fuel cell and other electrochemical device applications. The microcell technology is described in U.S. Pat. Nos. 5,916,514; 5,928,808; 5,989,300; and 6,004,691, all to Ray R. Eshraghi. The microcell structure described in these patents comprises hollow fiber structures with which electrochemical cell components are associated.
The aforementioned Eshraghi patents describe an electrochemical cell structure in which the single cell is formed of a fiber containing an electrode or active material thereof, a porous membrane separator, electrolyte and a second electrode or active material thereof. Cell designs are described in the Eshraghi patents in which adjacent single fibers are utilized, one containing an electrode or active material thereof, the separator and electrolyte, with the second fiber comprising a second electrode, whereby the adjacent fibers constitute positive and negative electrodes of a cell.
The present invention embodies additional advances in the Eshraghi microcell technology.
This invention relates to microcell electrochemical devices and assemblies, methods of making same by various techniques, and use of such devices and assemblies.
In one aspect, the invention relates to an electrochemical cell module, comprising:
a multiplicity of microcells in an assembly,
each microcell comprising an inner electrode,
a microporous membrane separator in contact with the inner electrode,
an electrolyte in pores of the microporous membrane separator,
an outer electrode,
with the microcell assembly including a plurality of hollow tubular heat exchange elements arranged for flow of a coolant medium through a central lumen thereof, with the hollow tubular heat exchange elements being distributed in such assembly for heat removal from the assembly during electrochemical reaction in operation of the module;
a source of the coolant medium; and
flow circuitry interconnecting the source of the coolant medium and the hollow tubular heat exchange elements.
Another aspect of the invention relates to an electrochemical cell module, comprising:
a multiplicity of microcells in an assembly,
each microcell comprising an inner electrode,
a microporous membrane separator in contact with the inner electrode,
an electrolyte in pores of the microporous membrane separator, and
an outer electrode,
wherein the assembly is mounted in a housing, and oriented along an axis of the housing, with a first end potted in a first potting member through which open ends of the microcell fibers are exposed for fluid flow therethrough, with the first potting member isolating the shell side of the microcell fibers from the bore side thereof, and with current collectors constituting heat exchange elements and extending axially of the first potting member and further potted in a second potting member in spaced relationship to the first potting member, to define between the first and second potting members a closed volume of the housing, and with a housing inlet communicating with the closed volume, for introduction of feed into the closed volume, for flow through the assembly on the bore side of the microcell fibers thereof, and wherein the second potting member defines with the housing a closed end volume, with the current collectors constituting heat exchange elements extending through the second potting member and terminating in the closed end volume at open ends thereof, and with a coolant medium inlet communicating with the closed end volume, for introduction of coolant medium into the closed end volume for flow through the current collectors constituting heat exchange elements, to remove heat of electrochemical reaction from the assembly;
with a second end of the assembly potted in an opposite potting member through which open opposite ends of the microcell fibers are exposed for fluid flow therethrough, with the opposite potting member isolating the shell side of the microcell fibers from the bore side thereof, and with opposite current collectors extending axially of the opposite potting member and current collections constituting heat exchange elements terminating at the opposite potting number, and with a housing outlet communicating with the closed volume, for discharge of depleted fuel and coolant medium from the closed volume, for removal of heat of electrochemical reaction from the assembly;
and wherein the current collectors at their ends are joined in series or parallel with one another to form a terminal leak-tightly extending out of the housing.
A still further aspect of the invention relates to an electrochemical cell module, comprising:
a multiplicity of microcells in an assembly,
each microcell comprising an inner electrode,
a microporous membrane separator in contact with the inner electrode,
an electrolyte in pores of the microporous membrane separator,
an outer electrode,
wherein the assembly is mounted in a housing, and oriented along an axis of the housing, with a first end potted in a potting member through which open ends of the microcell fibers are exposed for fluid flow therethrough, with the potting member isolating the shell side of the microcell fibers from the bore side thereof to form a closed end volume, and with current collectors constituting heat exchange elements and extending axially of the potting member into the closed end volume, and coupled to at least one heat exchange passage in the housing, with such at least one heat exchange passage being arranged for flow of a coolant medium therethrough, and with a housing inlet communicating with the closed end volume, for introduction of feed into the closed end volume, for flow through the assembly on the bore side of the microcell fibers thereof;
with a second end of the assembly potted in an opposite potting member through which open opposite ends of the microcell fibers are exposed for fluid flow therethrough, with the opposite potting member isolating the shell side of the microcell fibers from the bore side thereof to form a closed end volume isolating the shell side of the microcell fibers from the bore side thereof, and with current collectors constituting heat exchange elements and extending axially of the opposite potting member into the closed end volume, and coupled to at least one second heat exchange passage in the housing, with said at least one second heat exchange passage being arranged for flow of a coolant medium therethrough, and with a housing outlet communicating with the closed end volume, for discharge of depleted fuel from the closed end volume;
and wherein the current collectors at their ends are joined in series or parallel with one another to form a terminal leak-tightly extending out of the housing.
Yet another aspect of the invention relates to an electrochemical cell module, comprising:
a multiplicity of microcells in an assembly,
each microcell comprising an inner electrode active material,
a microporous membrane separator in contact with the inner electrode active element,
an electrolyte in pores of the microporous membrane separator,
an outer electrode active element,
with each of the inner and outer electrode active elements comprising at least one of electrode, current collector and electrocatalyst components, and such assembly including electrode or current collector components extending externally of the assembly to end portions thereof;
wherein the assembly is contained in a housing including a coolant reservoir;
a coolant in the coolant reservoir; and
the end portions of the electrode or current collector components being coupled in solid heat conduction relationship with said coolant, to enable solid conduction transfer of heat from the assembly of microcells through said electrode or current collector components to the coolant, to thereby remove heat generated by electrochemical reaction in said microcells during operation of the module.
In another aspect, the invention relates to a microcell module comprising an assembly of microcells wherein each microcell includes:
an inner electrode active material,
a microporous membrane separator in contact with the inner electrode active element,
an electrolyte in pores of the microporous membrane separator, and
an outer electrode active element,
with each of the inner and outer electrode active elements comprising at least one of electrode, current collector and electrocatalyst components, and said microcell including an elongate electrode or current collector;
means for extracting heat from the assembly selected from the group consisting of:
(a) hollow tubular heat exchange elements extending through the assembly of microcells, wherein said tubular heat exchange elements do not constitute current collectors;
(b) hollow tubular heat exchange elements extending through the assembly of microcells, wherein said tubular heat exchange elements constitute current collectors; and
(c) solid current collectors extending from the assembly of microcells and coupled in heat exchange relationship with a coolant medium.
In one process aspect, the invention relates to a process for generating electrochemical energy, comprising:
(A) providing an electrochemical cell module, comprising:
a multiplicity of microcells in an assembly,
each microcell comprising an inner electrode,
a microporous membrane separator in contact with the inner electrode,
an electrolyte in pores of the microporous membrane separator,
an outer electrode,
with the microcell assembly including a plurality of hollow tubular heat exchange elements arranged for flow of a coolant medium through a central lumen thereof, with the hollow tubular heat exchange elements being distributed in said assembly for heat removal from the assembly during electrochemical reaction in operation of the module;
a source of the coolant medium;
flow circuitry interconnecting the source of said coolant medium and said hollow tubular heat exchange elements;
(B) providing fuel to the electrochemical cell module to one of the shell side and bore side of the microcells in said assembly;
(C) concurrently providing oxidant to the electrochemical cell module to the opposite one of the shell side and bore side of the microcells in said assembly, relative to the side receiving fuel, and thereby effecting electrochemical reaction to generate electrical energy and heat;
(D) discharging depleted feed from the electrochemical cell module;
(E) flowing the coolant medium from said source of same through said flow circuitry and said hollow tubular heat exchange elements to remove heat from the electrochemical cell module;
(F) discharging said coolant medium from the module.
A further aspect of the invention relates to a method of thermally managing operation of an electrochemical cell module comprising:
a multiplicity of microcells in an assembly,
each microcell comprising an inner electrode,
a microporous membrane separator in contact with the inner electrode,
an electrolyte in pores of the microporous membrane separator,
an outer electrode,
the method comprising disposing in the microcell assembly a plurality of hollow fiber heat exchange elements arranged for flow of a coolant medium through a central lumen thereof, with the hollow fiber heat exchange elements being distributed in said assembly for heat removal from the assembly during electrochemical reaction in operation of the module; and
flowing a coolant medium through the hollow fiber heat exchange elements during electrochemical reaction in the microcell assembly.
A still further aspect of the invention relates to a method of generating electrochemical energy, including the steps of:
fabricating an electrochemical cell module comprising a plurality of fibrous microcell elements in an assembly including internal and external current collectors extending outwardly therefrom;
operating said electrochemical cell module to generate electrochemical energy; and
extracting heat from at least one of said internal and external current collectors during said operating, to thereby remove heat of electrochemical reaction from said electrochemical cell module.
Another aspect of the invention relates to a method of generating electrochemical energy in an electrochemical cell module, wherein the electrochemical cell module comprises: a multiplicity of microcells in an assembly, each microcell comprising an inner electrode active material, a microporous membrane separator in contact with the inner electrode active element, an electrolyte in pores of the microporous membrane separator, and an outer electrode active element, with each of the inner and outer electrode active elements comprising at least one of electrode, current collector and electrocatalyst components, and the assembly includes electrode or current collector components extending externally of the assembly to end portions thereof;
the method comprising:
mounting the assembly in a housing including a coolant reservoir with the end portions of said electrode or current collector components positioned in the reservoir; and
providing a coolant in the coolant reservoir to immerse the end portions of the electrode or current collector elements in the coolant, to enable solid conduction transfer of heat from the assembly of microcells through the electrode or current collector components to the coolant, to thereby remove heat generated by electrochemical reaction in said microcells during operation of the module.
Still another aspect of the invention relates to a method of thermal management of a microcell module comprising an assembly of microcells wherein each microcell includes:
an inner electrode active material,
a microporous membrane separator in contact with the inner electrode active element,
an electrolyte in pores of the microporous membrane separator, and
an outer electrode active element,
with each of the inner and outer electrode active elements comprising at least one of electrode, current collector and electrocatalyst components, and the microcell including an elongate electrode or current collector;
the method comprising extracting heat from the assembly by use of a means selected from the group consisting of:
(a) hollow tubular heat exchange elements extending through the assembly of microcells, wherein said tubular heat exchange elements do not constitute current collectors;
(b) hollow tubular heat exchange elements extending through the assembly of microcells, wherein said tubular heat exchange elements constitute current collectors; and
(c) solid current collectors extending from the assembly of microcells and coupled in heat exchange relationship with a coolant medium.
Other aspects, features and embodiments will be more fully apparent from the ensuing disclosure and appended claims.